1. Field of the Invention
This invention relates to parafoil aircraft, and more particularly concerns parafoil aircraft having a parafoil canopy that is inflated with lighter-than-air gas to a degree that provides vertical takeoff and landing (VTOL) capability.
2. Description of the Prior Art
A parafoil is a flexible structure made of lightweight fabric or similar material having a shape similar to an airplane wing or airfoil.
Aircraft using parafoils to generate lift are well known. Inflatable parafoils are also known. U.S. Pat. Nos. 4,934,630; 4,860,970; 4,557,439 and 4,424,945 describe parafoils that are inflated during flight by air rammed into apertures generally located at the leading edge of the parafoil. They do not use lighter-than-air gas for inflation, and they do not have VTOL capability.
U.S. Pat. No. 5,620,153 describes a parafoil canopy which is inflated with buoyant gas such as heated air or helium so as to provide at least partial lift. It does not describe a VTOL aircraft.
U.S. Pat. No. 5,005,783 describes a variable geometry airship that is essentially a dirigible balloon equipped with retractable inflatable wings so that it can also be flown like an airplane.
U.S. Pat. No. 5,090,637 discloses a helium purification system for lighter-than-air aircraft aimed mainly at removing oxygen and nitrogen when mixed with the helium in the aerostat to improve lift. The catalytic system described generates heat as a by-product which generates additional lift by heating the lift gas. It does not describe controlled variation of the displacement volume of the aircraft itself as a means for controlling lift, nor does it describe a parafoil aircraft in general or a VTOL parafoil aircraft in particular.
It may be seen that the prior art does not describe a VTOL parafoil aircraft wherein buoyancy is controlled by varying the outer envelope volume of the parafoil by use of a lighter-than-air inflating gas. A further drawback of current parafoil wings is that as horizontal speed increases, the parafoil canopy will lag further and further behind the suspended passenger module, and tends to function more as a drag chute than an airfoil wing. Like a drag chute, present parafoils tend to develop a downwardly directed concavity in their undersurface during flight. Such concavity entraps air and causes considerable drag.
It is accordingly a primary object of this invention to provide a parafoil aircraft with VTOL and hovering capability.
Another object of the present invention is to provide a parafoil wing capable of maintaining a streamlined shape and smooth surface with low drag and high aerodynamic efficiency suitable for cruising at higher speeds.
A further object of this invention is to provide a VTOL aircraft that can be manufactured easily and inexpensively and can be operated simply, safely and economically.
These objects and other objects and advantages of the invention will be apparent from the following description.
The above and other beneficial objects and advantages are accomplished in accordance with the present invention by an aircraft comprising a parafoil wing which, when fully inflated with buoyant gas, will generate sufficient lift to permit vertical takeoff, and when partially deflated will enable the aircraft to hover or make a slow and controlled vertical descent and landing.
The buoyant gas is deployed in three sets of independently inflatable compartments, namely, an upper compartment disposed on the entire upper surface of the parafoil, a lower compartment disposed on the entire lower surface, and a control, third variably inflatable compartment between the two. The upper and lower compartments are kept constantly tautly inflated so as to present a smooth external surface to the parafoil and give it a more defined and less deformable airfoil shape.
Chordwise stiffening ribs are placed at regular intervals from the leading edge to the trailing edge to prevent or diminish concave deformity of the undersurface, thereby diminishing drag and improving lift.